1. Field of the Invention
This invention relates to a positioning device for mounting a seat on a seat tube of a bicycle, more particularly to a positioning device which permits adjustment of the position of a seat on a seat tube of a bicycle.
2. Description of the Related Art
A conventional bicycle generally has a positioning device for mounting a seat on a seat tube of a bicycle and for adjusting the position of the seat relative to the seat tube in a front-and-rear direction so as to be suitable for different riders and to provide a feeling of comfort during riding.
Referring to FIGS. 1 and 2, a conventional positioning device 6 is used to mount a seat 7 on a seat tube 8 of a bicycle (not shown). The seat 7 includes two seat rails 71 each of which has a sliding segment 711 and two connecting segments 712 extending respectively from two ends of the sliding segment 711. The positioning device 6 includes a clamping unit 61 and a locking unit 62. The clamping unit 61 includes upper and lower clamping members 611, 612 which are disposed to respectively clamp the sliding segments 711 of the seat rails 71. The locking unit 62 is disposed to tighten the upper and lower clamping members 611, 612 together with the sliding segments 711.
During adjustment of the seat 7, the locking unit 62 is released to permit sliding of the clamping unit 6 along the sliding segments 711, so that the seat 7 can be moved relative to the seat tube 8 in a front-and-rear direction. However, the extent of adjustment of the seat 7 is limited by the configuration of the seat rails 71. If the length of the sliding segments 711 is increased to permit a greater extent of adjustment, the weight of the seat will be increased, which will adversely affect the bicycle.